Methods for locating a defect are known in which the medium is equipped with:                sources placed in said medium and adapted for emitting a wave in the medium, and        sensors placed in said medium and adapted for receiving said emitted wave.        
In particular, conventional imaging methods propagate acoustic or ultrasonic waves in a medium on different dates. Assuming that the propagation speed of the wave is known in the medium, it is possible to link a time to a distance and build up a reflectivity or reflectivity variation image at each point of the medium, showing the changes that have occurred between the two dates.
This type of method is effective for identifying heterogeneities or scatterers in a medium, when the wave is propagated in the medium in simple scattering regime, i.e. when, on its path, the wave only interacts with a single heterogeneity before being detected.
For a medium comprising numerous heterogeneities, such as concrete, the ultrasonic wave used in the aforementioned known method has a relatively low frequency of less than 50 kHz. However, when the detection of small defects included in such a heterogeneous medium is sought, this method is inefficient as the wavelength used is too large. Furthermore, the simple scattering regime method is not very sensitive as the ultrasonic wave only encounters the defect once on its path (travel) in the medium.
On the other hand, when the wave is propagated in the medium in multiple scattering regime in such a heterogeneous medium, i.e. when the wave interacts with several heterogeneities on its path before being detected, such a conventional imaging technique is no longer operational. It is no longer possible to associate a propagation time with a single path, nor to associate a path with a heterogeneity.